Chrysotile is the most commonly used asbestos mineral, and it clearly is the most cytotoxic, both in vitro and in vivo. There is good evidence that the elemental composition of chrysotile contributes to its cytotoxic nature. We have studied the translocation of Mg and Si ions from chrysotile fibers under the following experimental conditions: (1) After treatment with dehydrating agents, fixatives and embedding media, (2) After treatment with 1NHCL for 16 hours, (3) Following phagocytosis by alveolar macrophages, (4) After inhalation by rats. Transmission and scanning electron microscopy in concert with X-ray energy spectometry showed that significant amounts of Mg had slowly leached from asbestos fibers after one month in 2.5% glutaraldehyde. Treatment with 1NHCL caused a rapid (one hour) loss of significant Mg content which reached a plateau at about 4 hours. In contrast, two hours after phagocytosis by alveolar macrophages, no Mg loss was detected. Chrysotile fibers in the lungs of rats showed considerable variability in Mg content.